Kamal A. Idriss

Spectrophotometric study of the complexation equilibria of zirconium(IV) with 1-amino-4-hydroxyanthraquinone and the determination of zirconium

The spectral absorption and acid-base characteristics of 1-amino-4-hydroxyanthraquinone (AMHA) were studied in water-ethanol media. The composition, molar absorptivities, equilibrium constants and stability constants of the chelates of this reagent with zirconium(IV) have been determined spectrophotometrically in 40%V/V ethanol at 20 °C and an ionic strength of 0.1 M(NaClO4). Graphical logarithmic analysis of the absorbance graphs was used to demonstrate and characterise the complexation equilibria in solution. A simple, rapid, selective and sensitive method for the spectrophotometric determination of trace amounts of zirconium is proposed based on the formation of the Zr(AMHA)2 complex at pH 3.5 (λmax.= 600 nm, Iµ= 1.621 × 104 l mol–1 cm–1). Interference caused by a number of ions was masked by the addition of cyanide ions.

Acid dissociation and solution equilibria of some pyridinecarboxylic acids

The acid–base equilibria of 2-hydroxynicotinic acid (hyna), 2-mercaptonicotinic acid (mena), 3-hydroxypicolinic acid (hypa) and pyridine-2,3-dicarboxylic acid (quinolinic acid, quina) have been studied spectrophotometrically in a water–ethanol medium containing 23.5 mol-% ethanol at 20 °C. The solution spectra of these compounds have been recorded at different pH values and the spectral changes are explained in terms of shifts in equilibria between the different species that exist in solution. Two equilibria have been established in solutions at pH values of approximately 3–10.5, based on the acid dissociation of the non-ionized form (LH2) of the reagents. The existence of these equilibria is confirmed by potentiometric pH titrations. The release of the proton from the cationic form (LH3+) of substituted nicotinic acids was verified by measurements of the spectra at pH 0.5–2. The pKa values corresponding to various acid-base equilibria have been determined and are discussed in relation to molecular structure. Tautomeric equilibria of the type: neutral species ⇌ zwitterionic species, in solutions of hyna and mena, have also been characterized using the ionization constants of the two acids.

Solution equilibria and stability of the complexes of pyridinecarboxylic acids: Complexation reaction of mercury(II) with 2-hydroxynicotinic acid

SummaryThe solution equilibria of 2-hydroxynicotinic acid (hyna) complexes with mercury(II) have been studied spectrophotometrically in 50% (v/v) ethanol at 20°C and an ionic strength of 0.1mol dm−3 (NaClO4). Three mercuric complexes are formed in solution in dependence on the acidity of the medium. The basic characteristics of the different complexes are determined and the analytical aspects of the complexation reaction are demonstrated. A critical investigation has also been presented of the solution equilibria and stability of the mixed complex of mercury(II) withhyna and thiosalicylic acid (tsa). The various complex transitions leading to the formation of the 1 : 1 : 1 Hg(tsa)(hyna) ternary complex in solution are investigated. The non-charged mono-ligand complex Hg(hyna) is used for UV-spectrophotometric determination of mercury atpH 4.5–5 (λmax=325nm, ɛ=0.8·104lmol−1cm−1). The system obeyed Beers law up to 36.1 µg ml−1 of Hg(II). The optimum concentration range (Ringbom) is between 6 and 28.5µg ml−1. Interference caused by a number of ions was masked by the addition of fluoride ions.ZusammenfassungDie Lösungsgleichgewichte von 2-Hydroxynikotinsäure (hyna) mit Hg(II) wurde spektrophotometrisch in 50% (v/v) Ethanol bei 20°C und einer Ionenstärke von 0.1 mol dm−3 (NaClO4) untersucht. In Abhängigkeit von der Acidität des Mediums werden drei Quecksilberkomplexe gebildet. Die grundlegenden Charakteristika der Komplexe wurden bestimmt und die analytischen Aspekte aufgezeigt. Die gemischten Komplexe von Hg(II) mithyna und Thiosalicylsäure (tsa), insbesondere die verschiedenen Komplexübergänge zum ternären 1 : 1 : 1 Hg(tsa)(hyna)-Komplex, wurden ebenfalls untersucht. Der ungeladene Monoligandenkomplex Hg(hyna) kann beipH 4.5–5 zur UV-spektroskopischen Quecksilberbestimmung eingesetzt werden (λmax=325nm, ɛ=0.8·104lmol−1cm−1). Das System gehorcht bis zu einer Hg(II)-Konzentration von 36.1µgml−1 dem Beerschen Gesetz. Der optimale Konzentrationsbereich (Ringbom) liegt zwischen 6 und 28.5µgml−1. Interferenzen mit einer Reihe anderer Ionen konnten durch Maskierung mit Fluoridionen umgangen werden.

Reaction of mercury(II)-thiosalicylate complex with picolinic acid and ultraviolet spectrophotometric determination of mercury(II)

The monothiosalicylate complex of mercury(II) reacts with picolinic acid (PIC) to form a ternary complex which has an absorption maximum at 295 nm in 50%V/V ethanol-water in the pH range 6.3–7.5. Beers law is obeyed up to a 20.15 µg ml–1 concentration of HgII. The molar absorptivity of the ternary complex is 0.86 m2 mol–1 at 295 nm and the sensitivity for the HgII ion is 5.2 × 10–3µg cm–2 per 0.001 absorbance unit. The composition of the ternary complex is estimated to be Hg(TSA)(PIC). A number of ions which interfere with the determination could be masked by the addition of EDTA or fluoride ions as masking agents. Further information on the complex-forming equilibria and stability of the HgII ternary complex was obtained by potentiometric titrations at 20 ± 0.1 °C and 0.1 M(NaClO4) ionic strength.

Spectrophotometric study of the complexation equilibria of yttrium(III) with quinizarin green

The complexation equilibria of yttrium(III) with quinizarin green [1,4-bis(4′-methylanilino)anthraquinone] were studied spectrophotometrically in the presence of 40% dimethylformamide at 20 °C and an ionic strength of 0.1 M(NaClO4). The composition, molar absorptivities, equilibrium constants and stability constants of the complexes formed were determined using graphical analysis of the absorbance curves within the pH range studied. The optimum conditions for the spectrophotometric determination of Y(III) with this reagent were established.

5-Chlorosalicylic acid spectrophotometric method for the determination of titanium and simultaneous determination of titanium(IV) oxide and iron(III) oxide content of portland cement

A spectrophotometric study of the titanium(IV)–5-chlorosalicylic acid (CSA) reaction was carried out to ascertain the suitability of the titanium–CSA complex formed at pH 2.5–3 for the direct spectrophotometric determination of titanium. The method is simple and rapid and possesses reasonable selectivity. A linear calibration graph is obtained up to a concentration of 5.8 µg ml–1 of titanium. The optimum range for determination (Ringbom) is between 0.53 and 4.8 µg ml–1. The molar absorptivity and Sandells sensitivity are 1.9 × 104 l mol–1 cm–1 and 1.25 × 10–3µg cm–2, respectively, at 355 nm. Application of the method to the simultaneous determination of TiO2 and Fe2O3 in Portland cement was investigated. The absorbance at 510 nm, due to the iron(III)–CSA complex, is recommended for the determination of Fe2O3 in cement, whereas the characteristic absorption of the titanium complex at 355 nm is corrected for iron(III) present in the sample. The analysis of cement materials containing different proportions of titanium and iron is feasible over the concentration ranges 1.28–4.8 µg ml–1 Ti and 18.5–40.2 µg ml–1 Fe3+. The limits of detection (at the 95% confidence level) of the method are 12 and 36 ng ml–1 for titanium and iron, respectively. The individual determination of titanium in cement samples can also be achieved if iron(III) present in solution is masked by the addition of 0.01 mol l–1 ascorbic acid. The developed procedure was tested by analysing several samples and was found to give satisfactory results.

Direct spectrophotometric determination of aluminium oxide in Portland cement and cement clinker. An insight into the solution equilibria and analytical aspects of the aluminium–quinizarin system

A spectrophotometric study of the complexation reaction between Al3+ and quinizarin (QUIN) was carried out to ascertain the suitability of the complex formed for direct spectrophotometric determination of aluminium. The absorbance at 550 nm, due to the aluminium–QUIN complex, formed at pH 3.8, is recommended for the determination of the alumina content of Portland cement and cement clinker. The proposed method is simple and rapid and possesses reasonable selectivity. Interference of iron(III), generally present in Portland cement, is eliminated by addition of ascorbic acid. The results obtained for several SRM Portland cement samples and for a variety of cement materials demonstrate that the proposed method allows the precise and accurate determination of Al2O3 content over the concentration range 1.4–5.75 μg mL−1 of aluminium. The determination of Al can be carried out successfully in the absence of a masking agent by using first-derivative spectrophotometry. Verification and the use of control charts in the spectrophotometric determination of Al is achieved. The record of the verifier response during routine operation establishes that the method is being maintained in statistical control.

Acid–base characteristics of naphthazarin and solution equilibria of yttrium(III) chelates

The spectral absorption and acid–base characteristics of naphthazarin (5,8-dihydroxy-1,4-naphthoquinone; NAZA) in ethanol–water medium containing 50% v/v ethanol have been studied, and pKa values have been determined. Two equilibria are established in solution at pH 2.5–11.5, based on the acid dissociation of the non-ionized form of the reagent. The existence of these equilibria is confirmed by potentiometric pH titrations, and the precision of the equilibrium study is improved. The composition, molar absorptivities and stability constants of the chelates of NAZA with yttrium(III) have been determined by spectrophotometry under the conditions encountered in this study. The complexation equilibria existing in solution are demonstrated and characterized. The Y(NAZA) mono-ligand chelate formed at pH 5.5 (Iµ= 1.15 × 104 l mol–1 cm–1 at 595 nm) allows the determination of 1.95–8.86 µg ml–1 of yttrium. Interfering species and their elimination have been studied.

Rapid test methods for minor components analysis of hydraulic cement. Spectrophotometric determination of manganese oxide content of Portland cement and cement raw meal

A rapid, sensitive and highly selective spectrophotometric method for the determination of manganese oxide content of Portland cement and cement raw meal is developed. The method is based on the reaction of manganese(II) with 1,2,4 trihydroxyanthraquinone (purpurin, PURP) in 50% v/v ethanol-water solution at pH 8.5. The solution equilibria of manganese chelates are demonstrated and characterized for delineating optimal conditions of the complexation reaction and analytical aspect of the Mn-PURP system. The analysis of cement materials of variable manganese content is feasible over the concentration range 1.67-8.13 microg ml(-1) Mn, the limit of detection (at the 95% confidence level) of the method is 68 ng ml(-1) for manganese. Under optimum conditions, the use of first derivative spectrophotometry has the advantage of high sensitivity than normal spectrophotometric method and allows the determination of 0.5 microg ml(-1) of manganese.

An insight into the solution equilibria of magnesium(II) with purpurin and spectrophotometric determination of magnesium

The complexation equilibria of magnesium(II) with purpurin (PURP) are studied spectrophotometrically as a function of pH in 50% (v/v) ethanol-water medium at 20 degrees C. The uncharged complex formed at pH 9.5 allows precise and accurate determination of magnesium over the concentration range 0.8-4.3 mug ml(-1). The molar absorptivity of the Mg-PURP complex at 540 nm and detection limit for Mg are 9.2x10(3) l mol(-1) cm(-1) and 75 ng ml(-1), respectively. The proposed method is rapid and possesses reasonable selectivity. Under the optimum conditions, the use of first-derivative spectrophotometry has the advantage of high sensitivity than normal spectrophotometry and allows the determination of 0.2 mug ml(-1) of magnesium. The validity of the method is examined by analysing several SRM Portland cement samples and a variety of cement materials of variable magnesia content.